1. Field of the Invention
This invention relates to a bracket that is attached to a tooth for orthodontic treatment.
2. Description of the Related Art
Orthodontic treatment includes the application of mechanical forces to urge the teeth into correct position and proper alignment. Small, slotted bodies known as brackets are secured to the teeth, and a resilient archwire is seated in the bracket slots. The archwire is bent or twisted before installation in the slots in such a manner that the restoring force exerted by the wire tends to shift the teeth into orthodontically correct alignment.
In some instances, the relationship between the upper arch and the lower arch should be changed during orthodontic treatment to correct what are known as Class II or Class III malocclusions. To this end, small hooks are sometimes secured to appropriate brackets, to selected locations of the archwire, or to buccal tubes (which are similar to brackets but which are adapted to be secured to the molar teeth for anchoring the ends of the archwire). An elongated elastic member is connected to a hook on the upper arch and a hook on the lower arch, and has sufficient tension when in place to provide a resilient force in order and urge the upper arch either in an inward or an outward direction relative to the lower arch.
Hooks for correction of Class II and Class III malocclusions are often uni-directional hooks having a generally "J-shaped" configuration, and thus are adapted to hold the elastic member in place only when the member extends in a single predetermined direction which is either a generally mesial, or generally distal direction. However, bi-directional hooks have been sometimes provided in locations near the mid-point of the arch for permitting the elastic member to extend in either the mesial or the distal direction. The bi-directional hook can be initially used to correct a Class II or Class III malocclusion with an elastic member extending in one direction, and subsequently used with an elastic member extending in the opposite direction in order to align the midline of the upper arch with the midline of the lower arch during the final or finishing stages of orthodontic treatment.
In the past, certain bi-directional hooks have been known as ball hooks and include a stem with an enlarged, somewhat hemispherical head. Sometimes, ball hooks are brazed to the archwire or to a tiewing of a bracket. Some brackets made in a sintering operation or in a casting operation have ball hooks that are integrally connected with one of the tiewings of the bracket. However, ball hooks are not entirely satisfactory because the enlarged, hemispherical head often protrudes into the patient's cheeks and causes discomfort.
Occasionally, three-wing orthodontic brackets are used during orthodontic treatment. Three-wing brackets often have two spaced apart occlusal wings on the mesial and distal sides of the bracket, and a single, central gingival wing located in the middle of the gingival side of the bracket. Some three-wing brackets have integral gingival hooks extending from the single, central gingival wing, and the hooks have mesial and distal notches to provide a bi-directional capability. Such hooks are generally flat and have been found to reduce patient discomfort in the areas of the cheeks.
However, some orthodontists prefer twin brackets which have four tiewings rather than three-wing brackets because the brackets with four tiewings provide greater capability for enabling ligatures to exert rotational forces on the tooth about its long axis. Furthermore, brackets with four tiewings provide easier opportunities for using more than one elastic member on the bracket at the same time. As such, there is a need for a bracket having the capabilities of a bracket with four tiewings, but with a bi-directional hook that causes little, if any, patient discomfort.